Not Applicable.
Not Applicable.
Oscillators are used in a variety of electronic circuits, such as communication devices, to provide a variety of functions. These functions include, for example, the generation of a local oscillator signal. Radio communication devices, such as portable telephones and the like, require a stable operating frequency provided by the local oscillator. Typically, the output signal of the local oscillator is generated by a voltage controlled oscillator (VCO). It is often difficult to mass-produce such VCO circuits so that they all have the same basic operating frequency (i.e., the same relaxation frequency). This is due to the fact that the operating frequency is strongly dependent on parts tolerances and manufacturing techniques. In general, variation in component tolerance and parasitics as well as variation over temperature requires adjustment of the relaxation frequency in a post assembly process. More particularly, the resonant frequency of a tuned circuit is typically adjusted until the desired relaxation frequency is reached.
Tuned resonant circuits are used in oscillators, such as VCOs, to generate a free running signal at the relaxation frequency. Such resonant circuits are available in a variety of topologies. One commonly used tuned circuit topology employs a microstrip followed by an inductor that, in turn, forms a tuned circuit with a capacitor, which may be in the form of a varactor. The capacitor is frequently formed on a monolithic substrate with other components of the VCO while the inductor is often formed as a discrete component that is separate from the monolithic substrate where it is physically accessible during the manufacturing process. This particular topology is suitable for applications where relaxation frequency is adjusted during the VCO manufacturing process. More particularly, the resonant frequency of the tuned circuit is adjusted by laser trimming the externally disposed inductor/microstrip to vary its physical dimensions.
The trim range of the inductor/microstrip component is proportional to the effective length/width variation of the component resulting from the laser trimming process. This tuning range is constrained by the physical size of the component, the parasitic capacitance, and the degradation of Q factor caused by narrowing the line when tuning.
Current methods of inductive tuning use one or more cuts into a metallized area. This tuning method requires costly capital equipment and can be difficult to implement accurately. Such problems, among others, render this tuning style inefficient. An improved method of tuning resonators and corresponding circuit topology is therefore desired.
A programmable capacitive network for use in a tunable resonant circuit is set forth that may be used in a number of different applications, but is particularly useful in the tuning of a voltage controlled oscillator formed on a substrate, such as a semiconductor substrate or the like. The programmable capacitive network includes a plurality of capacitive elements. An interconnected network of voltage gate elements and fuse elements are interconnected with the capacitive elements to selectively connect one or more of the plurality of capacitive elements in the resonant circuit in response to at least one program control signal. In accordance with one embodiment, the voltage gate elements are diodes.